I think its Dark Cave, I have 2 platinum games.
Route 214
Route 214 and Valor Lakefront hope it helped :)
Its on the upper rock path first item easy to spot
After you have beaten the elite four and get the national pokedex you go to route 214.
ruin maniac's cave route 214 near veilstone city
Go to Route 214 and go in the ruin maniac cave.
route 214 near cave need rock smash.
The Ruin Maniac's Cave. Which is on the face of the mountain on Route 214.
The Magmarizer only appears on Route 214 on Pokemon Platinum. In Pokemon Platinum the Magmarizer can be found north of Ruinic Maniac Bryan on Route 214.
you find the magamarizer on route 214. it is not long away from the ruin maniacs cave
route 214
In Turnback Cave after Spring Path on route 214 (must find in cave after many rooms)
on route 214
route 214
route 214 below veilstone city
you can find it at route 214
Route 214